Electric furnace

ABSTRACT

In an electric furnace having an electric contact there are provided inner and outer metallic members carrying electricity, the inner intended to act as an axle or hub for the outer, and one of which is moving and the other stationary. Connecting them together and conducting electricity is a content of molten metal or alloy, typically mercury, an alkali metal or the like. The heat development is carried off by artificial cooling by conducting a liquid or gas through cooling passages.

United States Patent 1191 Verhoeven et al.

[ Man 5, 1974 ELECTRIC FURNACE [75] Inventors: Pierre Verhoeven,Bruxelles; Jean A. F. Sunnen, Waterloo; Henry R. P. J. Schoumaker,Bruxelles, all of Belgium 1 [73] Assignee: La Soudure ElectriqueAatogene,

Procedes Arcos, Anderlecht, Belgium [22] Filed: Apr. 25, 1973 [21]Appl.-N0.: 354,364

Related us. Application Data [62] Division of ser. No. 279,865, Aug. 11,1972.

52 us. CI. 13/1, 13/10 51 lnt.,Cl F27b 7/00, 1105b 7/18 58 Field ofSearch... 13/1, 9, 10

[56] References Cited UNITED STATES PATENTS 3,227,642 Lemelson 13/10 X11/1966 Foex 13/10 X 10/1970 Grosse 13/1 X Primary Examiner-Roy N.Envall, Jr. Attorney, Agent, or Firm -Jackson, Jackson and Chovanes [57ABSTRACT In an electric furnace having an electric contact there areprovided inner and outer metallic members carrying electricity, theinner intended to act as an axle or hub for the outer, and one of whichis moving and the other stationary. Connecting them together andconducting electricity is a content of molten metal or alloy, typicallymercury, an alkali metal or the like. The heat development is carriedoff by artificial cooling by conducting a liquid or gas throughcoolingpassages.

2 Claims, 18 Drawing Figures PAIENTEDHAR 51974 795'752 sum 1 er 7PATENTED "AR 51974 SHEEI 2 [IF 7 PATENTEDHAR 51914 SHEET 3 [IF 7PATENTEW 3,795,752

saw u or 7 FIG. IO

ELECTRIC FURNACE DISCLOSURE OF THE INVENTION This invention relates toan electric furnace and is a division of U.S. application Ser. No.279,865, filed Aug. 1 l, 1972 for Slip Ring. It relates to means forconducting electricity between stationary contacts and movable contact.

Among the numerous known means for transmitting electric current from afixed contact to a moving contact or vice versa, the simplest are thosewhich consist of a slip ring comprising a roller integral with one ofthe parts, which is put into contact with the other part under a certainpressure. If necessary, that pressure may be regulated by elastic means.

The fields in which electric current is transmitted are for instancethose of electric traction, which utilize an arm and a contact wheel(trolley) to pass the electric current to the vehicle to which the armis connected. Unfortunately these arrangements are far from being freefrom drawbacks. Owing to friction on the parts they heat up and undergoplastic deformation and are quickly worn out by erosion. These drawbacksare particularly serious at high speeds and high amperages, owing tovibrations, breaks in contact, and sparks produced as a result-of theamplitude and frequency of the oscillatory movements of the vehicle orthe mobile element as it undergoes movement. At high speeds elasticmeans for regulating the pressure when they are present, are not withoutinertia and they have not sufficient sensitivity to absorb the inertiareactions promptly enough.

The present invention contributes a radical remedy to these drawbacks.It consists of a process for transmitting electric current between astationary element and a movable element or vice versa, characterized bythe fact that the transmission is ensured by means which maintaincontact between the parts without friction and with maximum flexibility.This means consists in a device which has an electroconductive liquidinterposed between the mobile part and a fixed part.

The figures are accompanied by the present description and areillustrative only of some of the numerous forms of implementation of thedevice in accordance with the present invention, which clearly shows theobjects of the invention and its numerous advantages.

, In the various figures elements which are identical or similar areidentified by the same reference numbers.

FIG. 1 is a perspective of the invention in axial section. v

FIG. 2 is a perspective of another form of the invention, in axialsection.

FIG. 3 is a radial section of a form having an auxiliary deviceConnected to the device of the invention.

FIG. 4 is a partial transverse section of FIG. 3.

FIG. 5 is a perspective of another form of implementation of theinvention in axial section.

FIG. 6 is a partial transverse section on the line 6-6 of the deviceaccording to FIG. 5.

FIG. 7 is a plan of another example of the utilization of a slip ringaccording to the invention.

FIG. 8 is a plan of still another example of the slip ring according tothe invention, in transverse section.

FIG. 9 shows in transverse section a slip ring according to theinvention assembled at the aperture of a rotary furnace heated by aplasma column.

FIG. 10 is an installation diagram of two slip rings in accordance withthe present invention at the two extremities of a plasma rotatingfurnace.

FIG. 11 shows details of a slip ring mounted on the counter'electrode ofa l-torch rotating furnace.

FIG. 12 illustrates in axial section and diagrammatically the putting ofa non-consumable electrode into rotation by means of a slip ring inaccordance with the invention and animated by an electromagnetic field.

FIG. 13 is a transverse section diagrammatically of FIG. 12.

FIG. 14 is a diagrammatical view in longitudinal section of FIG. 12.

FIG. 15 is a perspective of a slip ring according to the invention intwo-plane section containing the axis.

FIG. 16 is a fragmentary sectional perspective of the fins.

FIG. 17 is a section transverse to the axis showing the fins.

FIG. 18 is an axial section with a diagrammatic illustration of thecirculation of a furnace according to the invention.

FIG. 1 illustrates a movable contact of slip ring 30 and a stationarycontact or hub 31 which is hollow and is carried by a hollow axle 32 incommunication with the hollow in the disc and around which the movablecontact 30 is able to fit rightly and turn freely.

Tightness is obtained by bearing seals 33 assembled in an insulatingtube in order to prevent the current passing through bearings 34. Thespace between the outside wall of the hollow disc 31 and the inside wallof the movable contact 30 is filled with electroconductive liquid 35.The hollow disc or contact 39 has inside and extending transverselyacross it a baffle 36 in the form of a solid disc centered on the hollowaxle and di viding the latter into two compartments 37 and 38 incommunication, each with a space separating the edge of the baffle andthe inner peripheral wall of the hollow disc. The purpose of the baffle36 is to divert toward the inside of the periphery of the hollow discthe flow of coolant fluid conveyed by the one axle 32 and taken away bythe other axle from the end.

Should there be a slight leakage of electroconductive fluid, the voidleft can be compensated by moving a finger or pin 40 entering theelectroconductive liquid and operated from the outside by a finethreaded screw 41 transversing the wall of the rotating contact 30; thispresupposes that the leak has been stopped.

Conversely, the finger 40 movement in the opposite direction is tocompensate for increase in volume of electroconductive liquid because ofexpansion caused by heat which is developed when the slip ring is inuse.

The example illustrated in FIG. 2 differs from that shown in FIG. 1 inthat the baffle is replaced by a solid central core 42 which is anintegral part of the axle 32 so that the space which is filled with theelectroconductive liquid 35 is no longer divided into two compartments.The core instead is pierced by a radial passage 43 and-43' respectivelyto provide inlet and outlet communications for coolant fluidcommunicated to the parts of the axle 32 in which coiled tubing 44immersed in the electroconductive liquid surrounds the core.

In the device shown in FIG. 3, the slip ring or mov-' able contact 30which is in any of the forms of the present invention, is placed betweenpoles 45 and 45 of electromagnetic coil 46 which is energized byelectric circuit 47 energized by source 48, so that when rotating thedifferent points of the lateral parts of the slip ring successivelytransverse in quadrature the magnetic field which is created between thepoles. Once the slip ring supplies voltage which is applied and once theslip ring is in motion, the magnetic field 50 combined in accordancewith the laws of electromagnetism with the electric current passing theslip ring in the direction shown by the vector 51 of FIGS. 3 and 4 togive rise to forces52 which act on the electroconductive liquid. Theeffect of this is to increasethe motion of the particles of the latterand improve the coolant effect.

The magnetic field will be at the same frequency and in phase with thecurrent transmitted. The current supplied by the electromagnetic coil issupplied by a source 48 synchronized by known means with a main source53.

It goes withoutsaying that the stationary system ca- 7 pable ofinducting agitation forces in the electroconductor liquid may be used inplace of the electromagnetic system which has just been described.

In a special form of implementation shown in FIG. 5, a separate conduit54 is placed in the hollow axle and coaxially to it. The conduit is incommunication with the most distant compartment 55 of the hollow disc,owing to a central hole 56 of the baffle to which the conduit is fixedby its end. As the compartment has no outlet by the axle, the coolantfluid conveyed in one direction is thus diverted toward the walls ofcompartment 55, passing into the other compartment 57 after havingcirculated around the baffle 36 in the opposite direction and is finallysucked. out in counterflow through the annular space 58 separated by theaxle wall from the central tube.

The current intensities to be transmitted are very high, and it isuseful to increase the contact surface between ,the slip 'ring and theopposite part (rail or wheel). In that case the rim of the slip ring isvery thin and sufficiently elastic to be able to bend under the pressureof the slip ring against the part.

In FIGS. 7 and 8 this effect is shown since the parts 60 or 61 cominginto contact with the slip ring 30 provide a deformed area of the slipring.

Needless to say, the moving rim is advantageously taking its profiledshape from the shape or the nature of the part of the work with which itmust come into contact. It may have a recess or guiding groove over allof the height of its contour, but it can also have a protrusion allalong the contour.

Mercury or one or another of the metals or alloys whose melting point islower than the temperature that can be reached by the slip ring rim maybe used as the electroconductive liquid, ensuring the transmission ofthe electric current between the moving part and the fixed part of theslip ring.

Apart from the alkali metals or the alkaline earth metals or the alloysof either, a whole series of alloys of this kind exists. For example,Woods metal (alloy) melts at 71 C. and is entirely suitable.

Before using mercury, one must be sure that it will not form an amalgamwith the metal with which it comes in contact. As it forms an alloy,then everything with which the mercury will come in contact must have aprotective coating. 7

One field in which the slip ring of the invention may find applicationis that in which the electric current to be transmitted is utilized witha view to making high temperatures available.

The slip ring of the invention can be replaced by a rotating metal disc,cooled if necessary, utilized as a nonconsumable electrode in theinstallation described in Belgian patent No. 410,281. ln addition therotation of the moving part of the slip ring will usefully be effectedby electromagnetic, induction.

Again the slip ring of the; invention can beused for melting operationsin a vacuum or protective atmosphere in melting refractory metals,particularly titanium. In the case in question the cooling of the slipring in accordance with the invention must be the subject of veryspecial attention from a corrosion point of view.

The use of water as a coolant fluid, for example, is not free fromtrouble. Should the coolant water circuit come in contact with thetitanium or other liquid metal contained in the hollow part, there is arisk of explosion, as titanium decomposes water into hydrogen andoxygen. That is why it will be preferable in such a case to choose as 'ameansof cooling the slip ring, mercury or liquid sodium circulating in aclosed circuit constituted by the electrode, the axial support and aheat exchanger outside the vessel containing the titanium.

Comparative measurements were taken of FR losses atthe level of the slipring of the invention and a conventional contact shoe.

With the slip' ring of the invention, the voltage drop measured at slipring level was 0.3 volt with a current of 1,240 amperes. With aconventional shoe the voltage drop measured at the shoe level was 0.36volt at a curpitting was The basic application describes a process fortransmitting electric current between a stationary component and amoving one, characterized in such transmissionbeing assured withoutfriction and with maximum smoothness, by means of an electroconductiveliquid joining an outer moving part to an inner fixed part provided withcooling means, the electric current direction going equally well fromthe fixed part to the moving part or vice v ersa.

In the special slip rings which are referred to therein, it is always acentral part (the coolant system included) which is fixed and theperipheric hollow part which is moving.

lt quickly appeared, however, that in numerous applications it wouldbe'more advantageous to have the peripheric part fixed, the central partbeing associated with the motion of a unit or even set in motion withoutthe assistance of a usual mechanical means (torque transmission).

Thus the sealing problems occurring at the level of the plasma torchfeeding rotating furnaces, similar to those in French patents Nos.1,405,958 and 1,526,999

functioning at high temperatures, are simplified when the torch nozzlestake part in the rotation of the vessel; the seals are then reduced tothe sizes of said nozzles which are cooled from the outside through thefixed part of the slip rings.

In addition, in cases where such furnaces are working continuously andin a conditioned atmosphere (for example, oxidizing, reducing, etc.) thevolume of the intermediate lock between the torch and the furnaceapertures only depends on the need to supply the materials beingtreated.

Finally, in the case of furnaces with a single torch, withcounter-electrode, such as are described in U.S. Pat. No. 3,300,561, thecounter-electrode can take the form of a rotating ring, possibly of aconductive refractory oxide compatible with the material to be treated;electrical contact is ensured by a small wheel in accordance with theinvention as described at greater length below.

Furthermore, the rotation of the central part, in accordance with theinvention, by non-mechanical means can be transmitted to an arc cuttingelectrode of the type described in German Pat. No. 53,678 (Belgian Pat.No. 410,281 and U.S. Pat. Nos. 2,355,838 and 2,815,435) or to thenon-consumable rotating electrode of an installation of the typedescribed in British Pat. No. 1,240,547 (U.S Pat. No. 3,420,939), theslip ring ensuring both the rotation of the axle and the transmission ofthe arc current.

The present invention consists of a special model of slip ring, for theapplication of the process covered by Belgian patent application 112,451, the axial part being put in rotation by mechanical or othertorque in accordance with special means, the fixed peripheral partreceives the electrical current from the outside and transmits it to theaxial part by an interposed electroconductive liquid.

In FIG. 9 the central metallic part 70 is part of the same structure asthe casing of a rotary furnace 71 indicated diagrammatically and withthe venturi 72 of a plasma torch for which it is to serve as a nozzle,the whole being set in rotation by the furnace.

The hollow metallic casing 73 is fixed and in contact with a positivepole of the direct current source 74, the negative pole being connectedto a cathode 75 of the torch which is also fixed.

This casing 73 is cooled by internal water circulation, the feeding pipe76 of which is non-conductive of electricity.

Between the moving part 70 and the fixed part 73 are inserted bearings76' insulated by non-conductive seals 77, and mercury fills the cavity78, insuring current transmission between the parts 70 and 73.

The plasma 80 generated in the nozzle spurts directly into the rotaryfurnace 71.

In FIG. the nozzles 82, 82' of the two plasma torches are assembledsolid, to the ends of the rotary furnace 83, the driving and rollingmembers of which are not shown.

A plasma column spurts into the furnace vessel when the electriccircuits 85, 85' (pilot currents) and ionization energy current closedbetween fixed contacts 87 and 87 on the one hand the rotary nozzles 82and 82 on the other hand by means of a fixed wheel 88 and 88',plasmagene gas being introduced into the annular space of the torches asshown by the arrows.

FIG. 11 shows in detail the assembly of a slip ring 90 of an electricfurnace 91 showing the electric current, the counter-electrode of therotary furnace of the plasma torch of which is placed at the oppositeend (not shown) as in FIG. 2. The seal 92 is as in the precedingfigures, an insulating part.

In this case the plasma column can be animated in the furnace vessel byan incorporated electromagnetic field rotating so as to displace the arcimpact on the disc of the counter-electrode and reduce corrosion of thesame.

In FIG. 12 the electrical system is shown at 89, the inner disc 93 ofthe slip ring is set in rotation by a rotating field affixed by means ofelectromagnetic windings 94 of the appropriate electricalcharacteristics and frequency incorporated in the fixed water cooledcasing 95 containing the mercury 96.

The integral axle 97 of the disc rotates the insulated bearing 98 andtransmits rotation and are current to the non-consumable rotatingelectrode 100 of a fusion furnace 101 (partly shown) similar to that ofBritish Pat. No. 1,240,547 (U.S. Pat. No. 3,420,939).

In FIGS. 13 and 14 the same slip ring is simply sketched in at 98,depicts motion of the axle 97 of an arc cutting wheel 100 to an ingotmold 101 (Belgian Pat. 410,281 and U.S. Pat. No. 2,007,225).

SECOND IMPROVEMENT In the basic application it is disclosed that it ispossible to utilize the slip ring as a non-consumable electrode in afurnace, in a vacuum or inert atmosphere, in the fusion of metals and inparticular of titanium according to British Pat. No. 1,240,547.

However, taking into account the danger of explosion, reservations aremade and it is recommended to use a liquid metal such as mercury orliquid sodium as a coolant.

The present invention constitutes a noteworthy improvement on a slipring, bearing in mind these limitations. It is particularly importantfor fusion equipment, in a vacuum or controlled atmosphere, particularlyunder reduced pressure, and in which such a slip ring is utilized as anon-consumable electrode.

The said improved slip ring is characterized by the fact that the liquidmetal is put in circulation and simultaneously ensures:

l. A spin of the hollow cylinder constitutes the periphery of the slipring by action of a liquid metal on the fins fitted inside the hollowcylinder.

2. The electric contact between the fixed center part and the rotatinghollow cylinder.

3. The cooling of the rotating hollow cylinder.

The equipment comprises:

a. Circuit transversed by the liquid metal outside the furnace properwith a pump, heat exchanger, fixed contact for current input andadequate current sources. I

b. The furnace proper with a slip ring, a fixed connection at theoutside circuit transversed by the liquid metal and all the necessaryknown means such as cooled ingot mold, return of current to earth,supply of material. to be melted, supply of inert gas, and means forholding the vessel below atmospheric pressure.

FIG. 15 is a view of the structure of the invention in which mercury orother conducting liquid is introduced under pressure by the axial tubeand distributed by the injectors 111 over the center part 112 to thefins 113 which are integral with the movable housing 114. Under theaction of the mercury flow this part is set spinning. The mercury isreturned by the evacuation ring 115 coaxial to the axial tube 110.

It is important to note that the center part identified by numbers 110,115, 112 is not rotating; the only mobile part 114 is free on the shaft115 through the bearings 117. Current is fed in at 118 through fixedshaft 115, the bearings 117 being electrically insulated at 120 fromshaft 115.

FIGS. 16 and 17 show an arrangement of fins 113 and injector nozzles 111of a mercury mini-turbine, in

which the mercury streams are 125 and 126.

The circuitry of the equipment is sketched in FIG. 18. The vessel of thefurnace 127 is shown schematically as well as the ingot mold 128, thehopper 130 supplying the metal to be melted and the vessel conditioningpump 131. g

Passing shaft 132 of the slip ring electrode 133 is sealed bearing 134greatly simplified, as this shaft is-not rotating. It will, therefore,be particularly easy to make it electrically insulated and perfectlytight at 134. The liquid is put into circulation by the pump 131 toensure rotation of the slip ring since inner tube 135 is made to rotate,explained in FIGS. 15, 16, '17. The conductor liquid is cooled by heatexchanger 136. The electric current is fed to fixed shaft 132 at 137 byjaws which arelfixed mechanically'or brazed intoshaftl32r Arc 138 isstruck by known means, for instance a high frequency pilot dischargebetween cylindrical surface 140 and the molten metal in the metal poolin the ingot mold 128. The outer flow of the conductive liquid is fromshaft 132 to pump 131 and heat exchanger 136 which is at the potentialof the slip ring electrode insulated from the ground. However, there isno problem as the voltages used are relatively low and generally lessthan 1,000 volts.

In view of our invention and disclosure, variations and modifications tomeet individual whim or particu: lar need will doubtless become evidentto others skilled in the art to obtain all or part of thebenefits of ourinvention without copying the process and apparatus shown, and we,therefore, claim all such insofar as they a fall within the reasonablespirit and scope of ourtclaims.

We claim:

'1. In a furnace, a furnace body of tubular cross section havingopenings at the end adapted to receive a plasma jet, a venturi atone endin line with the jet opening, a cathode in the venturi, a metalliccentral part leading from the venturi to the opening in the end" of thefurnace, having a direct opening at the center and having a disk-likecontour on the outside, a hollow metallic casing around the disk-likeportion and around the casing and the, far end of the plasma jetand-means cooling the casing.

2. A furnace of claim 1, which has seals between a rotating central partand an inmovable casing, there being on the perimeter of the casingmeans for making electrical contact to a moving surface of the centralpart.

1. In a furnace, a furnace body of tubular cross section having openings at the end adapted to receive a plasma jet, a venturi at one end in line with the jet opening, a cathode in the venturi, a metallic central part leading from the venturi to the opening in the end of the furnace, having a direct opening at the center and having a disk-like contour on the outside, a hollow metallic casing around the disk-like portion and around the central opening, the casing making with the central part a sealed space, an electroconductive molten metal in this space between the central part and the casing, Means to provide a plasma jet in the venturi, means to provide an electric circuit including a power source between the cathode and the casing and means to provide an electric circuit including a power source between the casing and the far end of the plasma jet and means cooling the casing.
 2. A furnace of claim 1, which has seals between a rotating central part and an inmovable casing, there being on the perimeter of the casing means for making electrical contact to a moving surface of the central part. 